Means for photoelectrically scanning balanced sound records



Aug. 29, 1939.

G. 'CLAMANN MEANS FOR PHOTOELEGTRI-CALLY SCANNING BALANCED SOUND RECORDS Filed NOV. 15, 1937 fzderzior Jr @ez/zcmi (Kama/m Patented Aug. 29, 1939 UNITED STATES PATENT OFFHCE Gerhard Glamann, Dresden, Germany, assignor to Zeiss Ikon Aktiengesellschaft, Dresden, Germany Application November 15, 1937, Serial No. 174,606 In Germany November 23, 1936 5 Claims.

The invention relates to means for photoelectrically scanning balanced sound records. Sound records of this type are produced by separately recording the positive half-waves and the negative half-waves respectively of the oscillations to be recorded. For the reproduction these records are scanned separately and after having been scanned, they are combined to produce the original oscillation. Since the two sound tracks containing the two half-waves are locally separated on the record carrier, consisting for instance of a film, and since in other respects these two halfwave records are complete equivalent of each other, the recombination of the two records upon reproduction necessitates the inversion of the phase of one of these half-wave records.

It is an object of the present invention to provide a novel system suitable for this purpose. It is characterized by the fact that two light sensitive elements are employed which as to direct current are connected in parallel, with the terminals of the same polarity connected with each other, while at the same time the two light sensitive elements are connected as to alternating current, in opposition to each other and serially. Preferably, the two light sensitive elements are combined and arranged in a single vessel wherein both cathodes of the photoelectric tubes constituting the light sensitive elements are united to form a single cathode common to the two anodes.

The electric systems used heretofore for the scanning of balanced sound records have certain defects which are eliminated by the system of the present invention. The defects of the prior system are to be ascribed primarily to the fact that a transformer has to be used as a coupling element between the light sensitized elements on one hand and the amplifier on the other hand. This transformer is extremely sensitive to any magnetic disturbances, owing to its great number of windings and owing to the amplification to which the voltage is subjected.

The present invention eliminates also the disadvantages which are inherent in those systems wherein a photoelectric tube requires a positive voltage with respect to its cathode, while a second photoelectric tube requires a negative voltage with respect to its cathode, and wherein furthermore these voltages are of such value that the available amplifier is not able to furnish the same; hence these voltages must be generated by special means.

It also has been proposed heretofore to employ systems in which two photoelectric tubes are connected in series as for the direct current, but in these systems a high positive voltage with respect to the cathode is required equal to the double value of the negative voltage.

The drawing consisting of Figs. 1 to 4 illustrates by way of example embodiments of. the novel system of the invention:

In the drawing, l indicates the amplifier tube to which is coupled a double photoelectric tube 2 suitable for scanning a balanced double track sound. record. The photoelectric tube 2 by way of example is provided with a single cathode 3 and two anodes 4 and 5. Coupling condensers are indicated at 6 and 1, and resistors at 8 and 9. The two other resistors I0 and II serve the purpose of connecting the anodes with a negative voltage, which is supplied by the conductor l2. It is, however, also possible to supply each of the two anodes 4 and 5 with a separate voltage through its respective resistor I0 and II respectively (Fig. 2). If these voltages are made variable, it is convenient to balance the two opposite halves.

The operation of these circuits will become readily comprehensive by assuming the space between the electrodes 3 and 4 and also the space between the electrodes 3 and 5, to be the location of a source of alternating current whose potential is rapidly varied with the frequency the light impulses entering the tube. When the sum of the reactances consisting of the coupling condenser and coupling resistances 9, or coupling condenser E and the coupling resistance 8 respectively, is substantially smaller than the opposing force presented by the resistor II or III respectively, the currents generated by said alternating current source will flow principally through the coupling condenser 'l and the coupling resistances 9 or through the coupling condenser 6 and the coupling resistor 9 respectively, and thereby will cause a voltage drop in opposite direction within the resistors 8 or 9 respectively, said drop of potential being also applied to the grid of the amplifier tube I, as will be readily understood.

It may here be stated that the circuits shown in the drawing may be varied in a number of ways but all of such variations are included within the scope of the inventive principle outlined above. It will also be understood that the two halves instead of. being balanced by varying the potentials, may for instance also be balanced by the insertion of variable light absorbing elements I! (Fig. 4) into the path of the light rays directed toward the photoelectric tube.

What I claim is:

1. A system for photoelectrically scanning balanced two track sound records, including in a circuit two light sensitive elements, one for each of said two sound tracks, means for connecting said two light sensitive elements as to direct current parallel to each other, with like polarities connected with each other, while connecting said light sensitive elements as to alternating current in opposition to each other and in series, said means including two serially arranged resistances, one for each said two light sensitive elements and arranged to combine the output of the same, a single amplifier tube, and means for directly connecting the outer ends of said two serially arranged resistances with said amplifier tube.

2. A system for photoelectrically scanning balanced two track sound records, including in a circuit two light sensitive means, one for each of said two sound tracks, means for connecting said two light sensitive means as to direct current parallel to each other, with like polarities connected with each other, while also connecting said light sensitive means as to alternating current in opposition to each other and in series, said means including two serially arranged resistances, one for each said two light sensitive means and arranged to combine the output of the same, a single amplifier tube, and means for directly connecting the outer ends of said two serially arranged resistances with said amplifier tube, said light sensitive means consisting of. a photoelectric tube including within a vessel two separate anodes and a single cathode common to both said anodes.

3. A system for photoelectrically scanning balanced two track sound records, including in a circuit two light sensitive means, one for each of said two sound tracks, means for connecting said two light sensitive means as to direct current parallel to each other, with like polarities connected with each other, while connecting said photoelectric means as to alternating current in opposition to each other in series, and a single amplifier tube directly connected with said connecting means and having a grid to which the voltage drop in said connecting means is applied, said light sensitive means consisting of a photoelectric tube including within a vessel, two separate anodes and a single cathode common to both said anodes, and means within said circuit and connected with said anodes for supplying the same with variable potentials.

4. A system for photoelectrically scanning balanced two track sound records, including in a circuit two light sensitive means, one for each of said two sound tracks, and means for connecting said two light sensitive means as to direct current parallel to each other, with like polarities connected with each other, while connecting said light sensitive means as to alternating current in opposition to each other and in series, and variable light absorbing means arranged in the path of light leading to said photoelectric means.

5. A system for photoelectrically scanning balanced two track sound records, including in a circuit two light sensitive means, one for each of said two sound tracks, and means for connecting said two light sensitive means as to direct current parallel to each other, while connecting said light means as to alternating current in opposition to each other and in series, said light sensitive means consisting of a photoelectric tube including within a vessel, two separate anodes and a single cathode common to both said anodes, and variable light absorbing means arranged in the path of light leading to said photoelectric tube.

GERHARD CLAMANN. 

